Electroluminescent,photoemissive,charge storing memory matrix



Dec. 30, 1969 D, w` G. BYA'r-r 3,487,378

ELECTROLUMINESCENT, PHOTOEMISSIVE, CHARGE STORING MEMORY MATRIX FiledJune 14, 1967 INVENTOR www M15/,1 ma my ATTORNEYS United States Patent OU.S. Cl. 340-173 5 Claims ABSTRACT OF THE DISCLOSURE An electricalsignal storing device having on one side of its charge storing layer, anelectroluminescent layer sandwiched between two sets of grids of goldconductors, wherein signals applied between the grids in each set causethe electroluminescent layer to emit light and produce, via aphotoconductive layer, a signal representative charge pattern on thecharge storing layer, and having on the other side of its charge storinglayer a second electroluminescent layer sandwiched between two furthersets of grids between which signals are applied to cause theelectroluminescent layer to emit light and read off, via a secondphotoconductive layer, signals stored on the charge storing layer.

This invention relates to electrical signal storing devices and has forits object to provide improved, relatively simple and compact storingdevices of large capacity and reasonably fast access.

According to this invention in its broadest aspect an electrical signalstoring device comprises an electrical charge storing insulating layer,an electroluminescent layer, a photoemissive layer between saidinsulating layer and said electroluminescent layer, and means actuatableby signals to be stored for causing selected small portions of saidelectroluminescent layer to emit light, the whole arrangement being suchthat light emitted from said selected small portions of theelectroluminescent layer cause photoemission from the correspondingsmall portions of the photoemissive layer the resultant depletioncurrents being utilised to produce signal representative charges on saidinsulating layer. The charge-storing insulating layer may be a partiallylaterally conductive glass layer as normally employed as the chargestoring glass membrane or sheet of the target of a television cameratube of the Image Orthicon type.

In a preferred form of storing device in accordance with the inventionthe insulating layer is opaque to light emitted from the photoemissivelayer and there are provided, in addition to the layers alreadymentioned, a second electroluminescent layer on the side of saidinsulating layer remote from the iirst mentioned electroluminescentlayer, a photoconductive layer between said second electroluminescentlayer and said insulating layer, and electrical means for causingselected small portions of said second electroluminescent layer to emitlight thereby causing corresponding small portions of thephotoconductive layer to become conductive and provide paths to anoutput circuit for charges stored on the corresponding small portions ofsaid insulating layer.

The electroluminescent, photoemissive and photocon- 3,487,378 PatentedDec. 30, 1969 ICC ductive layers may each be a continuous layer butpreferably they are of so-called dot mosaic structure.

Light emission from selected small areas of an electroluminescent layerprovided in accordance with this invention is preferably produced byproviding said layer with sets of conductors on opposite sides thereof,the conductors of one set crossing (in projection) those of the otherand applying potential between two selected conductors, one in each set,to cause light emission from the small layer portion of saidelectroluminescent layer in the region of the shortest path between thetwo selected conductors.

A preferred embodiment of the invention comprises a central layer ofelectrical charge storing material (such as the felectrical chargestoring glass commonly employed in the target structure of a televisioncamera tube of the Image Orthicon type); a layer of photoelectricmaterial deposited on one side of the central layer; a layer ofphotoconductive material deposited on the other side of said centrallayer; a pair of light-transparent sheets of metal film one on the outerside of the photoelectric layer and one on the outer side of thephotoconductive layer; a pair of light transparent insulating spacers,one on each of the outer sides of the two metal iilm sheets; two gridseach of transparent parallel metal lilm conductors one on each of theouter sides of the said spacers; a pair of electroluminescent layers oneon each of the outer sides of said two grids; two further grids ofparallel conductors one on each of the outer sides of theelectroluminescent layers, the grids which are on opposite sides of thesame electroluminescent layer being composed of conductors which (inprojection) cross one another; a pair of insulating outer support andprotecting sheets, one on each of the outer sides of the said twofurther grids; and connection means to the individual conductors of thegrids and to the metal sheets.

The invention is illustrated in the accompanying in which FIGURE 1 is across-sectional schematic view showing the nature of the construction ofa preferred embodiment of the invention and FIGURE 2 is a diagramshowing the method of connection of the conductors of two grids onopposite sides of one of the electroluminescent layers in FIGURE 1. Itis emphasized that both figures, but especially FIGURE 1, are purelyschematic, no attempt being made in FIGURE 1 to show either the actualor the relative thicknesses of the various layers and conductorstherein.

Referring to FIGURE 1, and starting with the left hand side of thatFIGURE 1 is a glass supporting and protecting sheet, on the inner side(right hand side in FIGURE l) of which is a deposited grid 2 of straightmetal conductors which run parallel to one another. On the inner side ofthis grid is a layer 3 of electroluminescent material on the inner sideof which is deposited grid 4 of light transparent thin straight metaliilm conductors-for eX- ample of thin deposited goldrunning at rightangles to the conductors of the grid 2. On the inner side of the grid 4is a light transparent insulating spacer 5, e.g. of glass, on the inerface of which is a light-transparent conductive metal sheet `iilm 6 e.g.of thin deposited gold. On the inner face of this sheet is a layer 7 ofphotoemissive material the inner face of which is on the adjacent faceof a thin layer 8 of electric charge storing material. The member 8 maybe a thin sheet or membrane of glass, on the inner face of which is alight-transparent brane of the target of a television camera tube of theImage Orthicon type. Separate external connections are provided for thesheet conductor 6 and for the individual conductors of the grids 2 andy4.

The parts of the device as so far described constitute the parts whichare employed to produce on the layer 8 a stored charge patternrepresentative of signals to be stored. If a signal to be stored isapplied, in the form of a pulse of suitable value, between a selectedconductor of the grid 2 and a selected conductor of the grid 4, then asmall portion of the layer 3 lying in the shortest path between the twoselected conductors i,e. in their cross over region (in projection) willemit light which, passing through the grid 4, the spacer 5 and the sheet6 will cause photoemission from the corresponding small portion of thelayer 7. A positive potential is maintained across the said layer 7 by asuitable potential applied to the conductive sheet 6. Accordingly thephotoelectrons will be carried away and the depletion current from thephotoemissive material of the layer 7 will cause an electrical charge tobe produced on and stored by the correspondingly small portion of thestorage sheet 8. Thus, by applying signal potentials between diierentselected pairs of conductors, one conductor of any pair being in thegrid 2 and the other being in the grid 4, a signal representative chargepattern can be produced on the insulating layer 8 which acts as thestore. FIGURE 2 shows diagrammatically parts of the grids 2 and `4 onopposite faces of the electroluminescent layer 3. The incoming signalsto be stored are applied between selected conductors by means known perse, indicated as constituted by logic control arrangements L1 and L2 towhich the conductors are connected. Thus, if a suitable pulse is appliedbetween the conductor marked X and the conductor marked Y in FIGURE 2,light, will be emitted from the small portion of layer 3 indicated bythe letter Z,

Signals stored on the layer 8 could be picked off in various differentways. It would, for example, be possible to pick them off by scanningthe right hand side (in FIGURE l) of layer 8 by a cathode ray. In thepreferred embodiment of -FIGURE l, which embodiment is much more compactand simpler than any arrangement involving cathode ray scanning wouldbe, the stored signals are picked off by means of an arrangementsomewhat similar to that used for producing them. Referring again toFIGURE 1 the layer 8 is made of light opaque material and on its outerface (right hand face in FIG- URE 1) is a layer 9 of photoconductivematerial. On the outer face of layer 9 is a sheet 10 of thin, lighttransparent metal film, e.g. of thin deposited gold. On the outer sideof the sheet 10 is a second light transparent insulating spacer 11, e.g.of glass, on the outer side of which is a grid 12 of thin, straight,parallel, light transparent metal -lm conductors. On the outer side ofthe grid 12 is a second electroluminescent layer 13, like the layer 3,with a grid 14 of straight parallel conductors on its outer face. Theconductors of this grid run at right angles to those of the grid 12.Finally, on the outer face of the grid 14 is a second supporting andprotecting sheet 15 like the sheet 1 and separate connections areprovided to the conductors of grids 12 and 14 and to the conductivesheet 10.

To read olf a signal stored on the layer 8, a reading pulse from asuitable source (not shown) is applied between the appropriate selectedpair of conductors, one in the grid 12 and the other in the grid 14.This causes light emission from a selected small portion of layer 13 inthe neighbourhood of the cross-over point of the selected pair ofconductors and the correspondingly small portion of the photoconductivelayer 9 becomes conductive. Output is taken from the conductive sheet10, and it will be seen that, if a charge is present in the smallportion of layer 8 corresponding to the illuminated small portion oflayer 9, the output signal will be representative of that charge. StoredSignals are thus taken o i from layer 8 by suitably pulsing diferentselected pairs of electrodes (one in grid 12 and the other in grid 14)by means of a circuit arrangement which it is not necessary toillustrate since it is, practically speaking, the counterpart of that ofFIGURE 2.

Each of the layers 3, 7, 9 and 13 may be a continuous layer but in theinterests of improved resolution, it is preferred to form them, inmanner known per se, as dot mosaic structures rather than as continuousfilms.

The pick-up control circuit for taking off stored signals may, ifdesired, incorporate facilities for re-writing output signals back intothe store when required.

The illustrated store device is exceedingly compact and of highcapacity. It is believed that, in practice, it will be able to store asmany as a million bits in a store of square form on a side of only about12 inches.

I claim:

1. An electrical signal storing device comprising an electrical chargestoring insulating layer, an electroluminescent layer, a photo-emissivelayer between said insulating layer and said electroluminescent layer,and means actuatable by signals to be stored for causing selected smallportions of said electroluminescent layer to emit light, the wholearrangement being such that light emitted from said selected smallportions of the electroluminescent layer cause photoemission from thecorresponding small portions of the photoemissive layer the resultantdepletion currents being utilized to produce signal representativecharges on said insulating layer and wherein `the insulating layer isopaque to light emitted from the photoemissive layer and there areprovided, a second electroluminescent layer on the side of saidinsulating layer remote from the rst mentioned electroluminescent layer,a photoconductive layer between said second electroluminescent layer toemit light thereby causing corresponding small portions of thephotoconductive layer to become conductive and provide paths to an`output circuit for charges stored on the corresponding small portionsof said insulating layer.

2. A device as claimed in claim 1 wherein the charge storing insulatinglayer is a partially laterally conductive glass layer as normallyemployed as the charge storing glass membrane of the target of atelevision camera tube of the Image Orthicon type.

3. A device as claimed in claim 1 wherein the electroluminescent,photoemissive and photoconductive layers are of so-called dot mossaicstructure.

4. A device as claimed in claim 3 wherein, in order to produce lightemission from selected small areas of an electroluminescent layer saidlayer is provided with Sets of conductors on opposite sides thereof theconductors of one set crossing (in projection) those of the other andapplying potential between two selected conductors, one in each set, tocause light emission from the small layer portion of saidelectroluminescent layer in the region of the shortest path between thetwo selected conductors.

5. A device as claimed in claim 4 comprising a central layer ofelectrical charge storing material; a layer of photoelectric materialdeposited on one side of the central layer; a layer of photoconductivematerial deposited on the other side of said central layer; a pair oflighttransparent sheets of metal film one on the outer side of thephotoelectric layer and one on the outer side of the photoconductivelayer; a pair of light transparent insulating spacers, 1one on each ofthe outer sides of the two metal lm sheets; two grids each oftransparent parallel metal -lm conductors one on each of the outer sidesof the said spacers; a pair of electroluminescent layers one on each ofthe outer sides of said t-wo grids; two further grids of parallelconductors one on each of the outer sides of the electroluminescentlayers, the grids which are on opposite sides of the sameelectroluminescent layer being composed of conductors which (inprojection) cross one another; a pair of insulating outer support andprotecting sheets, one on each of the outer sides of the said twofurther grids; and connection means to the indi- 5 6 vidual conductorsof the grids and to the metal lm 3,341,856 9/ 1967 Bigelow 346-74 h t. see s Refemces Cited BERNARD KONICK, Primary Examiner UNITED STATESPATENTS 1E. BREiMAYER, Assistant Examiner 5 3,125,741 3/1964 Kenneauy340-173 X US- Cl- X-R- 3,341,826 9/1967 Lee 340-173 340-166; 313-108

